Layered piezoelectric element realizing stable operating characteristic for high quality image recording

ABSTRACT

A layered piezoelectric element includes a plurality of driving parts divided by grooves and non-driving parts formed at both ends of the array of the driving parts. The driving parts and the non-driving parts include the alternate layers of piezoelectric layers and internal electrodes. The common electrode of the driving parts is extended from the non-driving parts. The capacitance C (F) of each driving part, the number of the driving parts n, and the resistance R (Ω) between the non-driving parts satisfy R≦8×10 −6 /n/C.

TECHNICAL FIELD

The present invention generally relates to image recording, and moreparticularly to a layered piezoelectric element, a method ofmanufacturing the same, a piezoelectric actuator, a liquid dropletejecting head, and an ink-jet recording apparatus.

BACKGROUND ART

An ink-jet recording apparatus employed as an image recording apparatus(an imaging apparatus) such as a printer, a facsimile machine, a copier,or a plotter includes an ink-jet head as a liquid droplet ejecting headincluding nozzles for ejecting ink droplets, liquid chambers (alsoreferred to as ink channels, ejection chambers, pressure chambers,pressure liquid chambers, or channels) communicating with the nozzles,and driving parts (pressure generating parts) for pressurizing ink inthe liquid chambers. Liquid droplet ejecting heads include a headejecting droplets of a liquid resist and a head ejecting droplets of aDNA sample in addition to an ink-jet head, but the following descriptionis given based mainly on the ink-jet head as the liquid droplet ejectinghead.

As an ink-jet head, a so-called piezoelectric ink-jet head is wellknown. The piezoelectric ink-jet head employs a piezoelectric body,particularly a layered piezoelectric body of alternate layers ofpiezoelectric layers and internal electrodes, as a pressure generationpart generating pressure for pressurizing ink in a liquid chamber. Anelastically deformable diaphragm forming a wall face of the liquidchamber is deformed by the displacement of the layered piezoelectricelement in the d33 direction, so that the volume/pressure inside theliquid chamber is changed, thereby ejecting ink droplets.

Japanese Laid-Open Patent Application No. 10-286951 discloses an ink-jethead using such a layered piezoelectric element. In this ink-jet head,grooves are formed in part of a layered piezoelectric element having anexternal electrode formed as individual electrodes on one side and acommon external electrode formed on the other side, so that a pluralityof driving parts (driving channels) are formed between non-driving partsformed on both ends. The common electrode of the layered piezoelectricelement extends from the non-driving parts on both ends in thedirections in which the driving parts are arranged.

In recent years, the ink-jet recording apparatus has been required toperform image recording with higher quality at higher speeds. In orderto increase recording speed, the number of nozzles of a head isincreased in the secondary scanning direction so that a single scan of acarriage in the primary scanning direction has a larger width in thesecondary scanning direction in printing.

However, in the case of extending the common electrode of the drivingparts of the layered piezoelectric element from the non-driving parts onboth longitudinal ends thereof as in the above-described ink-jet head,when the layered piezoelectric element is elongated so as to increasethe number of driving parts (driving channels) for the purpose ofincreasing recording speed, the length of conduction from the commonelectrode extension parts (non-driving parts) to each of the drivingchannels increases as the number of driving channels increases. As aresult, the resistance of the common electrode increases. Particularly,in the case of forming a plurality of driving parts by performinghalf-cutting on the layered piezoelectric element, the ungroovedremaining part serves as the common external electrode, so that the longnarrow part increases the resistance of the common electrode.

The time constant of a driving voltage applied to a driving channel inthe case of driving all the driving channels is different from that inthe case of driving only one of the driving channels.

The time constant of the driving voltage increases as the number ofdriving channels increases. Further, the degree of such increase becomesgreater as the resistance of the common electrode increases.

When the time constant of the driving voltage thus changes, an inkdroplet ejection characteristic, particularly ink droplet velocity,changes to vary the point of impact of an ink droplet. Therefore, whenthere is a large difference between the time constants of the foregoingtwo cases, great degradation is caused in image quality especially inthe case of printing a high-density image of approximately 600 dpi.

Therefore, in the conventional ink-jet head using a layeredpiezoelectric element, there is the problem that high image qualitycannot be obtained due to the large resistance of the common electrodeespecially in the case of printing a high-density image of approximately600 dpi.

DISCLOSURE OF THE INVENTION

Accordingly, it is a general object of the present invention to realizeimage recording in which the above-described disadvantage is eliminated.

A more specific object of the present invention is to provide a layeredpiezoelectric element reducing the difference between the time constantof a driving voltage in the case of driving all channels and that in thecase of driving only one channel, and a method of manufacturing thesame.

Another more specific object of the present invention is to provide apiezoelectric actuator having a stable operating characteristic, aliquid droplet ejecting head having a stable ejection characteristic,and an ink-jet recording apparatus capable of high-quality recording.

The above objects of the present invention are achieved by a layeredpiezoelectric element including: a plurality of driving parts divided bygrooves, the driving parts including alternate layers of piezoelectriclayers and internal electrodes; and non-driving parts formed at bothends of an array of the driving parts, the non-driving parts includingthe alternate layers of the piezoelectric layers and the internalelectrodes, wherein a common electrode of the driving parts is extendedfrom the non-driving parts, and a capacitance C (F) of each of thedriving parts, the number of the driving parts n, and a resistance R (Ω)between the non-driving parts satisfy R≦8×10⁻⁶/n/C.

The above-described layered piezoelectric element satisfies theexpression R≦8×10⁻⁶/n/C. Therefore, the difference in its operatingcharacteristic between the case of driving all channels and the case ofdriving one channel is reduced.

The above objects of the present invention are also achieved by alayered piezoelectric element including: a plurality of driving partsdivided by grooves, the driving parts including alternate layers ofpiezoelectric layers and internal electrodes; non-driving parts formedat both ends of an array of the driving parts, the non-driving partsincluding the alternate layers of the piezoelectric layers and theinternal electrodes; and an internal electrode for conduction connectedto a common external electrode of the driving parts and undivided by thegrooves, wherein a common electrode of the driving parts is extendedfrom the non-driving parts.

The above-described layered piezoelectric element includes the internalelectrode for conduction connected to the common external electrode ofthe driving parts. Therefore, the common electrode resistance isdecreased, so that the difference in its operating characteristicbetween the case of driving all channels and the case of driving onechannel is reduced.

The above objects of the present invention are also achieved by alayered piezoelectric element including: a plurality of driving partsdivided by grooves, the driving parts including alternate layers ofpiezoelectric layers and internal electrodes; non-driving parts formedat both ends of an array of the driving parts, the non-driving partsincluding the alternate layers of the piezoelectric layers and theinternal electrodes; and an external electrode for conduction connectedto a common external electrode of the driving parts, the externalelectrode for conduction being formed on a surface of the layeredpiezoelectric layer which surface is undivided by the grooves, wherein acommon electrode of the driving parts is extended from the non-drivingparts.

The above-described layered piezoelectric element includes the externalelectrode for conduction connected to the common external electrode ofthe driving parts. Therefore, the common electrode resistance isdecreased, so that the difference in its operating characteristicbetween the case of driving all channels and the case of driving onechannel is reduced.

The above objects of the present invention are also achieved by a methodof manufacturing a layered piezoelectric element including a pluralityof driving parts divided by grooves, non-driving parts formed at bothends of an array of the driving parts, and an internal electrode forconduction connected to a common external electrode of the driving partsand undivided by the grooves, the driving parts and the non-drivingparts including alternate layers of piezoelectric layers and internalelectrodes, the driving parts having a common electrode extended fromthe non-driving parts, the method including the steps of (a) fixing amember including a dummy part to a base, the dummy part being formed ofa piezoelectric layer to have a shape substantially symmetrical to ashape of a group of the internal electrodes of the alternate layers in adirection in which the alternate layers are formed, and (b) removing thedummy part from the member.

According to the above-described method, the layered piezoelectricelement of the present invention can be manufactured suitably with areduced warp.

The above objects of the present invention are also achieved by apiezoelectric actuator including a movable part and a layeredpiezoelectric element deforming the movable part, the layeredpiezoelectric element including: a plurality of driving parts divided bygrooves, the driving parts including alternate layers of piezoelectriclayers and internal electrodes; and non-driving parts formed at bothends of an array of the driving parts, the non-driving parts includingthe alternate layers of the piezoelectric layers and the internalelectrodes, wherein a common electrode of the driving parts is extendedfrom the non-driving parts, and a capacitance C (F) of each of thedriving parts, the number of the driving parts n, and a resistance R (Ω)between the non-driving parts satisfy R≦8×10⁻⁶/n/C.

The above objects of the present invention are also achieved by apiezoelectric actuator including a movable part and a layeredpiezoelectric element deforming the movable part, the layeredpiezoelectric element including: a plurality of driving parts divided bygrooves, the driving parts including alternate layers of piezoelectriclayers and internal electrodes; non-driving parts formed at both ends ofan array of the driving parts, the non-driving parts including thealternate layers of the piezoelectric layers and the internalelectrodes; and an internal electrode for conduction connected to acommon external electrode of the driving parts and undivided by thegrooves, wherein a common electrode of the driving parts is extendedfrom the non-driving parts.

The above objects of the present invention are also achieved by apiezoelectric actuator including a movable part and a layeredpiezoelectric element deforming the movable part, the layeredpiezoelectric element including: a plurality of driving parts divided bygrooves, the driving parts including alternate layers of piezoelectriclayers and internal electrodes; non-driving parts formed at both ends ofan array of the driving parts, the non-driving parts including thealternate layers of the piezoelectric layers and the internalelectrodes; and an external electrode for conduction connected to acommon external electrode of the driving parts, the external electrodefor conduction being formed on a surface of the layered piezoelectriclayer which surface is undivided by the grooves, wherein a commonelectrode of the driving parts is extended from the non-driving parts.

The above-described piezoelectric actuators each include the layeredpiezoelectric element of the present invention deforming the movablepart. Therefore, the above-described piezoelectric actuators can obtaina stable operating characteristic with reduced variation.

The above objects of the present invention are also achieved by a liquiddroplet ejecting head including a piezoelectric actuator pressurizing aliquid chamber communicating with a nozzle so as to eject a liquiddroplet from the nozzle, the piezoelectric actuator including a layeredpiezoelectric element, the layered piezoelectric element including: aplurality of driving parts divided by grooves, the driving partsincluding alternate layers of piezoelectric layers and internalelectrodes; and non-driving parts formed at both ends of an array of thedriving parts, the non-driving parts including the alternate layers ofthe piezoelectric layers and the internal electrodes, wherein a commonelectrode of the driving parts is extended from the non-driving parts,and a capacitance C (F) of each of the driving parts, the number of thedriving parts n, and a resistance R (Ω) between the non-driving partssatisfy R≦8×10⁻6/n/C.

The above objects of the present invention are also achieved by a liquiddroplet ejecting head including a piezoelectric actuator pressurizing aliquid chamber communicating with a nozzle so as to eject a liquiddroplet from the nozzle, the piezoelectric actuator including a layeredpiezoelectric element, the layered piezoelectric element including: aplurality of driving parts divided by grooves, the driving partsincluding alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of thedriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrodes; and an internalelectrode for conduction connected to a common external electrode of thedriving parts and undivided by the grooves, wherein a common electrodeof the driving parts is extended from the non-driving parts.

The above objects of the present invention are also achieved by a liquiddroplet ejecting head including a piezoelectric actuator pressurizing aliquid chamber communicating with a nozzle so as to eject a liquiddroplet from the nozzle, the piezoelectric actuator including a layeredpiezoelectric element, the layered piezoelectric element including: aplurality of driving parts divided by grooves, the driving partscomprising alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of thedriving parts, the non-driving parts including the alternate layers ofthe piezoelectric layers and the internal electrodes; and an externalelectrode for conduction connected to a common external electrode of thedriving parts, the external electrode for conduction being formed on asurface of the layered piezoelectric layer which surface is undivided bythe grooves, wherein a common electrode of the driving parts is extendedfrom the non-driving parts.

The above-described liquid droplet ejecting heads each include thepiezoelectric actuator of the present invention pressurizing liquidinside the liquid chamber. Therefore, the above-described liquid dropletejecting heads can obtain a stable operating characteristic with reducedvariation so as to be capable of performing image recording with highquality.

The above objects of the present invention are also achieved by anink-jet recording apparatus including an ink-jet head ejecting an inkdroplet, the ink-jet head including a piezoelectric actuatorpressurizing a liquid chamber communicating with a nozzle so as to ejectthe ink droplet from the nozzle, the piezoelectric actuator including alayered piezoelectric element, the layered piezoelectric elementincluding: a plurality of driving parts divided by grooves, the drivingparts including alternate layers of piezoelectric layers and internalelectrodes; and non-driving parts formed at both ends of an array of thedriving parts, the non-driving parts including the alternate layers ofthe piezoelectric layers and the internal electrodes, wherein a commonelectrode of the driving parts is extended from the non-driving parts,and a capacitance C (F) of each of the driving parts, the number of thedriving parts n, and a resistance R (Ω) between the non-driving partssatisfy R≦8×10⁻6/n/C.

The above objects of the present invention are also achieved by anink-jet recording apparatus including an ink-jet head ejecting an inkdroplet, the ink-jet head including a piezoelectric actuatorpressurizing a liquid chamber communicating with a nozzle so as to ejectthe ink droplet from the nozzle, the piezoelectric actuator including alayered piezoelectric element, the layered piezoelectric elementincluding: a plurality of driving parts divided by grooves, the drivingparts including alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of thedriving parts, the non-driving parts including the alternate layers ofthe piezoelectric layers and the internal electrodes; and an internalelectrode for conduction connected to a common external electrode of thedriving parts and undivided by the grooves, wherein a common electrodeof the driving parts is extended from the non-driving parts.

The above objects of the present invention are also achieved by anink-jet recording apparatus including an ink-jet head ejecting an inkdroplet, the ink-jet head including a piezoelectric actuatorpressurizing an ink chamber communicating with a nozzle so as to ejectthe ink droplet from the nozzle, the piezoelectric actuator including alayered piezoelectric element, the layered piezoelectric elementincluding: a plurality of driving parts divided by grooves, the drivingparts including alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of thedriving parts, the non-driving parts including the alternate layers ofthe piezoelectric layers and the internal electrodes; and an externalelectrode for conduction connected to a common external electrode of thedriving parts, the external electrode for conduction being formed on asurface of the layered piezoelectric layer which surface is undivided bythe grooves, wherein a common electrode of the driving parts is extendedfrom the non-driving parts.

The above-described ink-jet recording apparatuses each include theliquid (ink) droplet ejecting head of the present invention. Therefore,the above-described ink-jet recording apparatuses can perform stableimage recording with high quality.

The above objects of the present invention are further achieved by anink-jet recording apparatus including an ink-jet head, the ink-jet headincluding a layered piezoelectric element pressurizing a liquid chamberso as to eject an ink droplet therefrom, the layered piezoelectricelement including: a plurality of driving parts divided by grooves, thedriving parts including alternate layers of piezoelectric layers andinternal electrodes; and non-driving parts formed at both ends of anarray of the driving parts, the non-driving parts including thealternate layers of the piezoelectric layers and the internalelectrodes, wherein a common electrode of the driving parts is extendedfrom the non-driving parts, and a difference between a time constant ofa driving voltage applied to the layered piezoelectric element in a caseof driving all of the driving parts and a time constant of a drivingvoltage applied to the layered piezoelectric element in a case ofdriving one of the driving parts is smaller than or equal to 2 μsec.

The above-described ink-jet recording apparatus also reduces thedifference in its droplet ejection characteristics between the case ofdriving all channels and the case of driving one channel so as to becapable of performing image recording with high quality.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional view of an ink-jet head taken along directions inwhich a pressure liquid chamber thereof extends according to a firstembodiment of the present invention;

FIG. 2 is a sectional view of a layered piezoelectric element of theink-jet head of FIG. 1 taken along directions perpendicular to thedirections in which the pressure liquid chamber extends according to thefirst embodiment of the present invention;

FIG. 3 is a sectional view of a driving part of the layeredpiezoelectric element of the ink-jet head of FIG. 2 taken along the lineA—A;

FIG. 4 is a sectional view of a non-driving part of the layeredpiezoelectric element of the ink-jet head of FIG. 2 taken along the lineB—B;

FIGS. 5A and 5B are plan views of internal electrode patterns of thelayered piezoelectric element of the ink-jet head before processingaccording to the first embodiment of the present invention;

FIG. 6 is a perspective view of the layered piezoelectric element of theink-jet head taken from the common electrode side according to the firstembodiment of the present invention;

FIG. 7 is a perspective view of the layered piezoelectric element of theink-jet head taken from the individual electrode side according to thefirst embodiment of the present invention;

FIG. 8 is a diagram showing a circuit equivalent to an electricalcircuit from a driving waveform generating part to the layeredpiezoelectric element of the ink-jet head according to the firstembodiment of the present invention;

FIG. 9 is a diagram showing a simplified version of the equivalentcircuit of FIG. 8 according to the first embodiment of the presentinvention;

FIG. 10 is a graph for illustrating the difference between the timeconstant of a diving voltage in the case of driving all channels andthat in the case of driving one channel according to the firstembodiment of the present invention;

FIG. 11 is a graph for illustrating a relationship between the rise timeof the driving voltage and droplet ejection speed according to the firstembodiment of the present invention;

FIG. 12 is a sectional view of the layered piezoelectric element of anink-jet head taken along directions in which a pressure liquid chamberthereof extends according to a second embodiment of the presentinvention;

FIG. 13 is a sectional view of the layered piezoelectric element of theink-jet head of FIG. 12 taken along directions perpendicular to thedirections in which the pressure liquid chamber extends according to thesecond embodiment of the present invention;

FIG. 14 is a plan view of an internal electrode pattern for conductionof the layered piezoelectric element according to the second embodimentof the present invention;

FIG. 15 is a sectional view of the layered piezoelectric element of anink-jet head taken along directions in which a pressure liquid chamberthereof extends according to a third embodiment of the presentinvention;

FIG. 16 is a plan view of an internal electrode pattern for conductionof the layered piezoelectric element according to the third embodimentof the present invention;

FIG. 17 is a sectional view of the layered piezoelectric element of anink-jet head taken along directions in which a pressure liquid chamberthereof extends according to a fourth embodiment of the presentinvention;

FIG. 18 is a sectional view of an unprocessed layered piezoelectricelement to be processed into the layered piezoelectric element of anink-jet head for illustrating a method of manufacturing the layeredpiezoelectric element according to a fifth embodiment of the presentinvention;

FIG. 19 is a sectional view of the unprocessed layered piezoelectricelement for illustrating a method of manufacturing the layeredpiezoelectric element according to a sixth embodiment of the presentinvention;

FIG. 20 is a sectional view of the unprocessed layered piezoelectricelement for illustrating a method of manufacturing the layeredpiezoelectric element according to a seventh embodiment of the presentinvention;

FIGS. 21A and 21B are diagrams for illustrating an effect produced bythe manufacturing method according to the seventh embodiment of thepresent invention;

FIG. 22 is a sectional view of the layered piezoelectric element of anink-jet head taken along directions in which a pressure liquid chamberthereof extends according to an eighth embodiment of the presentinvention;

FIG. 23 is a sectional view of an ink-jet head taken along directions inwhich a pressure liquid chamber thereof extends according to a ninthembodiment of the present invention;

FIG. 24 is a perspective view of an ink-jet recording apparatusaccording to the ninth embodiment of the present invention; and

FIG. 25 is a side view of the ink-jet recording apparatus of FIG. 24showing a mechanism part thereof according to the ninth embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will now be given, with reference to the accompanyingdrawings, of embodiments of the present invention.

First Embodiment

First, a description will be given, with reference to FIG. 1, of anink-jet head as a liquid droplet ejecting head according to a firstembodiment of the present invention. FIG. 1 is a sectional view of theink-jet head taken along the directions in which the pressure liquidchamber 6 thereof extends.

The ink-jet head includes a channel substrate (liquid chamber substrate)1 formed of a single-crystal silicon substrate, a diaphragm 2 joined tothe lower face of the channel substrate 1, and a nozzle plate 3 joinedto the upper face of the channel substrate 1, thereby forming thepressure liquid chambers 6 and a common liquid chamber 8. The pressureliquid chambers 6 are channels (ink liquid chambers) with which nozzles5 ejecting ink droplets communicate through ink communicating channels 5a. The common liquid chamber 8 supplies ink to the pressure liquidchambers 6 via ink supply channels 7 serving as fluid resistance parts.

Through holes serving as the ink communicating channels 5 a and concaveparts serving as the pressure liquid chambers 6, the ink supply channels7, and the common liquid chamber 8 are formed in the channel substrate 1by performing anisotropic etching on a single-crystal silicon substrateof a (110) crystal plane using an alkaline etchant such as a potassiumhydroxide (KOH) aqueous solution.

The diaphragm 2 is formed of a plate of metal such as nickel. Thediaphragm 2 may also be formed of a resin member or a layered member ofresin and metal members.

The nozzles 5 of 10 through 30 μm are formed in the nozzle plate 3 so asto correspond to the pressure liquid chambers 6. The nozzle plate 3 isbonded to the channel substrate 1 with an adhesive agent. The nozzleplate 3 may be formed of metal such as stainless steel or nickel, acombination of metal and resin such as a polyimide resin film, silicon,or a combination of these materials. A water repellent film is formed onthe nozzle surface of the nozzle plate 3 by a well-known method such asplating or water repellent coating in order to ensure repellence againstink. The nozzle surface refers to a surface of the nozzle plate 3 in thedirection in which ink is ejected. The nozzle surface may also bereferred to as an ejection surface.

A layered piezoelectric element 12 is joined to the external face of thediaphragm 2 so that individual piezoelectric element parts of thelayered piezoelectric element 12 correspond to the pressure liquidchambers 6. The external face refers to a face of the diaphragm 2 on theopposite side from the pressure liquid chambers 6. The diaphragm 2 andthe layered piezoelectric element 12 form a piezoelectric actuatordeforming the diaphragm 2 that is a movable part.

The layered piezoelectric element 12 has a first face on one side joinedto the diaphragm 2 and a second face on the opposite side joined andfixed to a base 13 by an adhesive agent. Further, a side face of thelayered piezoelectric element 12 is connected to an FPC (flexibleprinted circuit) cable 14 for supplying driving waveforms to the layeredpiezoelectric element 12.

In this embodiment, the individual layered piezoelectric element partscorresponding to the respective pressure liquid chambers 6 are formed byforming slits in the long layered piezoelectric element 12. In thisspecification, “the overall length of a piezoelectric element” refers tothe length of the original long layered piezoelectric element 12 fromwhich the individual layered piezoelectric element parts are formed.

In this embodiment, ink inside the pressure liquid chambers 6 may bepressurized by using the displacement of the layered piezoelectricelement 12 in the d33 direction or in the d31 direction as itspiezoelectric direction.

As previously described, the layered piezoelectric element 12 has thesecond face joined and fixed to the base 13 by an adhesive agent. TheFPC cable 14 is joined by an adhesive agent to a face of the base 13which face is perpendicular to the face thereof joined to the layeredpiezoelectric element 12. The FPC cable 14 is further soldered directlyto individual external electrodes 24 of the layered piezoelectricelement 12.

It is preferable to use metal as material for the base 13. By usingmetal as material for the base 13, heat storage resulting fromself-heating of the layered piezoelectric element 12 can be preventedfrom occurring. The layered piezoelectric element 12 is joined to thebase 13 by an adhesive agent. As the number of channels increases,however, temperature rises near 100° C. due to self-heating of thelayered piezoelectric element 12 so as to reduce the joining strengthsignificantly. Further, the self-heating of the layered piezoelectricelement 12 increases temperature inside the ink-jet head so as toincrease ink temperature. The increase in ink temperature reduces inkviscosity, thus significantly affecting the ink ejection characteristicof the ink-jet head. Accordingly, by preventing the occurrence of heatstorage resulting from the self-heating of the layered piezoelectricelement 12 by forming the base 13 of a metal material, degradation ofthe ejection characteristic of the ink-jet head due to decrease in thejoining strength and the ink viscosity can be prevented.

When the base 13 has a large liner expansion coefficient, the adhesiveagent may peel off at the joining interface between the base 13 and thelayered piezoelectric element 12 at high or low temperatures. As to theconventional piezoelectric element, there seldom exists the problem ofpeeling off from the base 13 due to a difference in temperature causedby environmental variation since the piezoelectric element is shorter inoverall length. This problem has been made obvious by using apiezoelectric element that has approximately 40 nozzles at 300 dpi andis approximately 30 through 40 mm in overall length.

Accordingly, it is preferable to use a material having a linearexpansion coefficient of 10E-6° C. or lower for the base 13. By limitinglinear expansion coefficients to this range, the base 13 is preventedfrom peeling off from the piezoelectric element 12 at the joininginterface therewith due to a difference in temperature resulting fromenvironmental variation. It has been confirmed that it is very effectivein preventing peeling at the joining interface with a piezoelectricelement to set the linear expansion coefficient of each component joinedthereto to a value lower than or equal to 10E-6° C.

The FPC cable 14 includes a plurality of driver ICs 16 for applyingdriving waveforms (electrical signals) to drive the correspondingchannels (corresponding to the pressure liquid chambers 6). By providingthe driver ICs 16 to the FPC cable 14, electrical signal setting can beperformed independently in each of the driver ICs 16. This facilitatescorrection of variations in the displacement characteristics of thedriving channels of the layered piezoelectric element 12.

As the piezoelectric element becomes greater in length, it has been madeobvious that variations in the displacements of the channels becomegreater. Accordingly, by providing the driver ICs 16 to the FPC cable14, a variation in the displacement of the layered piezoelectric element12 is corrected by voltage in the channel directions (in which theindividual layered piezoelectric element parts are arranged), therebyrealizing a uniform ejection characteristic.

Further, a frame 17 is joined to the periphery of the diaphragm 2 by anadhesive agent. An ink supply channel 18 for supplying ink from theoutside to the common liquid chamber 8 is formed in the frame 17 acrossat least the base 13 from the driver ICs 16. The ink supply channel 18communicates with the common liquid chamber 8 via a through hole 2 a ofthe diaphragm 2.

The ink supply channel 18, the common liquid chamber 8, and the fluidresistance parts 7 are thus arranged on the opposite side from thedriver ICs 16 so that ink can be supplied from the opposite side fromthe FPC cable 14 connected to the layered piezoelectric element 12,thereby preventing a rise in ink temperature due to heating of thedriver ICs 16.

As previously described, the heat of the driver ICs 16, which may varydepending on the number of channels or driving waveforms, reaches around100° C. as the layered piezoelectric element 12 becomes larger inlength. When ink temperature rises due to the heating of the driver ICs16, ink viscosity decreases so as to significantly affect the ejectioncharacteristic. Therefore, the decrease in ink viscosity due to the risein temperature of the driver ICs 16 should be avoided by any means. Theheating of driver ICs is not so significant a problem in theconventional ink-jet head with a small number of channels. As theink-jet head becomes greater in length, however, the decrease in inkviscosity due to the rise in temperature of driver ICs has become aserious problem. This problem can be solved by employing theabove-described configuration.

A detailed description will be given herein, with reference to FIGS. 2through 7, of the layered piezoelectric element 12. FIG. 2 is asectional view of the layered piezoelectric element 12 of the ink-jethead of this embodiment taken along the directions perpendicular to thedirections in which the pressure liquid chamber 6 extends. FIG. 3 is asectional view of the layered piezoelectric element 12 of the ink-jethead of FIG. 2 taken along the line A—A. FIG. 4 is a sectional view ofthe layered piezoelectric element 12 of the ink-jet head of FIG. 2 takenalong the line B—B. FIGS. 5A and 5B are plan views of internal electrodepatterns of the layered piezoelectric element 12. FIG. 6 is aperspective view of the layered piezoelectric element 12 of the ink-jethead of this embodiment taken from the common electrode side. FIG. 7 isa perspective view of the layered piezoelectric element 12 of theink-jet head of this embodiment taken from the individual electrodeside.

In the layered piezoelectric element 12, a plurality of driving parts 25(individual piezoelectric element parts) are formed between non-drivingparts 26 on both ends of the array of the driving parts 25 by performingslitting or grooving processing on alternate layers of piezoelectriclayers (piezoelectric material layers) 21 and internal electrodes 22Aand 22B having pattern shapes as shown in FIGS. 5A and 5B, respectively,with a common external electrode 23 and the individual externalelectrodes 24 formed on the opposing longitudinal sides of the layerstructure. The common external electrode 23 is formed of the externalelectrodes on the common electrode side of the respective driving parts25.

In this slitting or grooving process, slits are formed in the layeredpiezoelectric element 12 so that a bridge part 27 of a size D in thedepth direction remains in the bottom of the layered piezoelectricelement 12 on the base 13. Further, a cutout 28 is formed on theindividual external electrode (24) side of the layered piezoelectricelement 12 along the directions in which the driving parts 25 arearranged.

Accordingly, the internal electrode 22A of each driving part 25 isconnected to the common external electrode 23, which is prevented frombeing divided due to the bridge part 27, so that the internal electrode22A of each driving part 25 is connected through the common externalelectrode 23 to the internal electrodes 22A of the non-driving parts 26on both ends. Further, the internal electrodes 22A of the non-drivingparts 26 extend to the individual external electrode (24) side of thelayered piezoelectric element 12 as shown in FIG. 4. Therefore, byconnecting the FPC cable 14 to the individual external electrode (24)side, the common electrode and the individual electrodes can be extendedfrom the one side of the layered piezoelectric element 12.

In the ink-jet head having the above-described configuration, a drivingpulse voltage of 20 to 50 V is applied to a selected one or more of thedriving parts 25 of the layered piezoelectric element 12 so that thedriving parts 25 to which the driving pulse voltage is applied stretchin the direction in which the layers are formed (that is, in the upwarddirection in FIGS. 2 through 4) so as to deform the diaphragm 2 towardthe nozzles 5. Thereby, the capacity or the volume of each correspondingpressure liquid chamber 6 changes so as to pressurize ink therein, sothat ink droplets are ejected (sprayed) from the corresponding nozzles5.

With the ejection of ink droplets, liquid pressure inside the pressureliquid chambers 6 decreases, so that a certain negative pressure isgenerated in the pressure liquid chambers 6 by the inertia of ink flowat this moment. By suspending application of the voltage to the layeredpiezoelectric element 12 in this state, the diaphragm 2 returns to itsoriginal position so as to restore the pressure liquid chambers 6 totheir original shape, thereby generating further negative pressure. Atthis point, ink flows through the ink supply channel 18, the commonliquid chamber 8, and the ink supply channels (fluid resistance parts) 7to be filled into the pressure liquid chambers 6. Then, after thevibrations of the ink meniscus surfaces of the nozzles 5 attenuate tostabilize, another pulse voltage is applied to the layered piezoelectricelement 12 for the next ejection of ink droplets, so that ink dropletsare ejected.

FIG. 8 is a diagram showing a circuit equivalent to an electricalcircuit from a driving waveform generating part to the layeredpiezoelectric element 12. As shown in FIG. 8, each driving part (drivingchannel) 25 is formed of a series circuit of a resistor (resistance)R_(on) (Ω) and a capacitor (capacitance) C (F), and the driving parts 25are connected with each other by resistors (resistances) R_(c)(Ω). Thecircuit of FIG. 8 is simplified so as to replace the resistors R_(c)with common electrode resistors (resistances) R_(com) (Ω) eachinterposed between the driving parts 25 and each non-driving part 26 asshown in FIG. 9.

When a pulse driving voltage P_(v) is applied, as shown in FIG. 10, tothe circuit of FIG. 9, letting the number of driving parts (drivingchannels) 25 be n, the time constant τ₁ (sec) of the driving voltageP_(v) applied to the driving part 25 in the case of driving only one ofthe n channels is given by the following equation (1):τ₁ =C(R _(on) +R _(com))  (1)

Further, the time constant τ_(all) (sec) of the driving pulse P_(v)applied to the driving parts 25 in the case of driving all the nchannels is given by the following equation (2):τ_(all) =C(R _(on) +n·R _(com)/2)  (2)

Accordingly, the difference Δτ between the time constant τ_(all) in thecase of driving all the n channels and the time constant τ₁ in the caseof driving only one of the n channels can be obtained from the followingequation (3):

$\begin{matrix}{{\Delta\tau} = {{\tau_{all} - \tau_{1}}\mspace{31mu} = {{{C( {R_{on} + {n \cdot {R_{com}/2}}} )} - {C( {R_{on} + R_{com}} )}}\mspace{31mu} = {{C( {{n/2} - 1} )} \cdot R_{com}}}}} & (3)\end{matrix}$

The equation (3) shows that as the number of driving channels n becomeslarger or the common electrode resistance R_(com) becomes larger, achange in the driving time constant τ becomes greater. That is, a changein the ink droplet ejection characteristic becomes greater.

On the other hand, the ink droplet ejection characteristic most affectedby the change in the time constant τ is an ejection velocity V_(j). Whenthe ejection velocity V_(j) changes, time required for an ink droplet tobe ejected from the ink-jet head to be positioned on a paper sheet (amedium onto which ink droplets are ejected) also changes. Since theink-jet head moves in the primary scanning direction, this changeultimately appears as a deviation of a dot position in the primaryscanning direction.

In the case of recording a 600-dpi image, when the deviation of a line(Δdot) exceeds approximately one dot, or 42.3 μm in distance, thedeviation is large enough to be visually recognized. Therefore, thedeviation is preferably smaller than or equal to 42.3 μm in terms ofhigher image quality.

Letting the ejection velocity in the case of driving all the n channels,the ejection velocity in the case of driving only one of the n channels,and the nozzle-paper distance be V_(jall), V_(j1), and L, respectively,the difference ΔT between time required for an ink droplet to travelfrom nozzle to paper in the case of driving all the n channels and thatin the case of driving only one of the n channels is given by thefollowing equation (4):ΔT=L/V _(jall) −L/V _(j1)  (4)

Further, letting scanning velocity for the primary scanning direction beV_(s), the deviation of a dot (Δdot) is given by the following equation(5):Δdot=ΔT×V _(s)=(L/V _(jall) −L/V _(j1))×V _(s)  (5)

Therefore, the ejection velocity V_(jall) in the case of driving all then channels is required to satisfy the following equation (6):V _(jall) =L/(Δdot/V _(s) +L/V _(j1))  (6)

When the ejection velocity V_(j) (m/sec) was measured with respect tothe rise time (μsec) of the driving voltage P_(v) with the primaryscanning velocity V_(s) and the nozzle-paper distance L being set to 0.4m/s (600 dpi) and 0.001 m, respectively, the characteristic as shown inFIG. 11 was obtained.

Here, if the ejection velocity V_(j1) in the case of driving only one ofthe n channels is set to 10 m/sec (τ₁=approximately 2 μlsec), in orderto set Δdot to a value smaller than or equal to 42.3 μm as previouslydescribed, the ejection velocity V_(jall) in the case of driving all then channels is required to be set to a value larger than or equal to 4.86m/sec, according to the above-described measurement results. Therefore,the time constant τ_(all) in the case of driving all the n channels isset to approximately 4 μsec.

Therefore, it is preferable to set the difference Δτ between the timeconstant τ_(all) and the time constant τ₁ to a value smaller than orequal to τ_(all)−τ₁=4−2=2 μsec. Thereby, the degradation of imagequality due to the deviation of a dot position can be prevented,particularly in the case of recording an approximately 600-dpi image.

Thus, in the layered piezoelectric element 12 of the ink-jet head ofthis embodiment, letting the capacitance of each driving part 25, thenumber of driving parts 25, and the resistance between the commonelectrode extension parts (non-driving parts 26) on both ends be C (F),n, and R (Ω), respectively, C (F), n, and R (Ω) satisfy the followingcondition (7):R≦8×10⁻⁶/n/C (7)

That is, based on the above-described equation (3), the followingexpression (8) should hold in order to satisfy Δτ ≦2 μsec in theejection characteristic.C(n/2−1)·R _(com)≦2×10⁻⁶  (8)

If the actuator is long so that n is sufficiently large, (n/2−1) can beregarded as n/2. Therefore, the above-described expression (8) can beconverted to the following expression (9):R _(com)≦4×10⁻⁶ /n/C  (9)

Since the resistance R between the common electrode extension parts ofthe layered piezoelectric element 12 is twice the resistance R_(com),the expression (9) can be expressed as the expression (7).

Thereby, the difference between the time constant of the driving voltageP_(v) applied in the case of driving one of the channels and the timeconstant of the driving voltage P_(v) applied in the case of driving allthe channels can be set to a value smaller than or equal to 2 μsec inthe ink-jet head of this embodiment. Thereby, variation in the ejectioncharacteristic of the ink-jet head is reduced so that a stablehigh-quality image can be obtained.

Second Embodiment

Next, a description will be given, with reference to FIGS. 12 through14, of an ink-jet head as a liquid droplet ejecting head according to asecond embodiment of the present invention. In the second embodiment,the same elements as those described in the first embodiment arereferred to by the same numerals. FIG. 12 is a sectional view of thelayered piezoelectric element 12 of the ink-jet head taken along thedirections in which the pressure liquid chamber thereof extends. FIG. 13is a sectional view of the layered piezoelectric element 12 of theink-jet head of this embodiment taken along the directions perpendicularto the directions in which the pressure liquid chamber extends (or thedirections in which the driving parts 25 are arranged). FIG. 14 is aplan view of an internal electrode pattern of the layered piezoelectricelement 12 according to this embodiment.

The layered piezoelectric element 12 of the second embodiment has aninternal electrode 30 for conduction provided in the bridge part 27,which is not divided by the grooving processing. The internal electrode30 has a pattern whose shape is equal to the planar outline of thelayered piezoelectric element 12 as shown in FIG. 14. In forming thelayered piezoelectric element 12, the internal electrode 30 can beformed easily in the bridge part 27 by forming the internal electrode 30between the piezoelectric layers 21 by printing when the internalelectrodes 22A and 22B are layered, printed on the green sheets servingas the piezoelectric layers 21.

The internal electrode 30 remains connected to the common externalelectrode 23 under the driving parts 25 after the grooving processing.Thereby, the channel of electricity widens greatly on the commonelectrode side so that the common electrode resistance can be reduced.The internal electrode 30 may have any shape as long as the internalelectrode 30 is connectable to the common external electrode 23 of thedriving parts 25 after the grooving processing. The wider the internalelectrode 30, the greater the desired effect of reduction in the commonelectrode resistance.

The internal electrode 30 for conduction that is not divided by thegrooving processing is thus provided so as to be connected to the commonexternal electrode 23. Thereby, the common electrode resistance isreduced, so that, as previously described, the difference between thetime constant of the driving voltage P_(v) applied to the layeredpiezoelectric element 12 in the case of driving one of the channels andthat in the case of driving all the channels can be set to a valuesmaller than or equal to 2 μsec. Thereby, the difference in the ejectioncharacteristic is reduced, so that a stable high-quality image can beobtained.

Third Embodiment

Next, a description will be given, with reference to FIGS. 15 and 16, ofan ink-jet head as a liquid droplet ejecting head according to a thirdembodiment of the present invention. In the third embodiment, the sameelements as those described in the first and second embodiments arereferred to by the same numerals. FIG. 15 is a sectional view of thelayered piezoelectric element 12 of the ink-jet head taken along thedirections in which the pressure liquid chamber thereof extends. FIG. 16is a plan view of an internal electrode pattern of the layeredpiezoelectric element 12 according to this embodiment.

The layered piezoelectric element 12 of the third embodiment has aninternal electrode 31 for conduction provided in the bridge part 27,which is not divided by the grooving processing, so as to be connectedto the common external electrode 23. As shown in FIG. 16, the internalelectrode 31 has a pattern whose shape is equal to that of the internalelectrode 22A.

Thereby, there is no need to prepare a special print pattern for theinternal electrode 31 for conduction, so that the manufacturingfacilities are simplified.

Fourth Embodiment

Next, a description will be given, with reference to FIG. 17, of anink-jet head as a liquid droplet ejecting head according to a fourthembodiment of the present invention. In the fourth embodiment, the sameelements as those described in the first through third embodiments arereferred to by the same numerals. FIG. 17 is a sectional view of thelayered piezoelectric element 12 of the ink-jet head taken along thedirections in which the pressure liquid chamber thereof extends.

The layered piezoelectric element 12 of the fourth embodiment has theinternal electrodes 30 for conduction of the second embodiment providedin a plurality of layers in the bridge part 27, which is not divided bythe grooving processing, so as to be connected to the common externalelectrode 23. The internal electrodes 30 may be replaced by the internalelectrodes 31 of the third embodiment or internal electrodes havinganother pattern shape.

By thus providing the internal electrodes 30 in a plurality of layers,the common electrode resistance can be further reduced. Normally, thethickness of the internal electrode is subject to limitation due to amanufacturing method. Therefore, it is not easy to increase the internalelectrode in thickness so as to reduce resistance. Further, the internalelectrode, which, generally, is formed of a palladium-silver alloy, hasa high volume resistivity compared with gold or copper used for theexternal electrode. Accordingly, a single internal electrode layer forconduction can reduce the common external electrode resistance only to alimited extent. Even when a plurality of internal electrode layers areprovided as in this embodiment, the thickness between the internalelectrode layers can be as small as approximately 20 μm. Therefore, anadverse effect such as increase in the thickness of a piezoelectric bodycan be reduced.

Fifth Embodiment

Next, a description will be given, with reference to FIG. 18, of amethod of manufacturing the layered piezoelectric element 12 accordingto a fifth embodiment of the present invention. FIG. 18 is a sectionalview of an unprocessed layered piezoelectric element 32, which is amember to be processed into the layered piezoelectric element 12.

According to the manufacturing method of the fifth embodiment, first,the unprocessed layered piezoelectric element 32 including a dummy part33 is formed. The dummy part 33 is formed of a piezoelectric layer to besubstantially symmetric in shape to the group of the internal electrodes22A and 22B (or the structure of the internal electrodes 22A and 22Bwith the corresponding piezoelectric layers 21) in the direction inwhich the layers are formed. Then, after fixing the unprocessed layeredpiezoelectric element 32 to the base 13, the dummy part 33 is ground tothe finishing line C shown in FIG. 18, so that the layered piezoelectricelement 12 of FIG. 12 is formed. The unprocessed layered piezoelectricelement 32 can also be formed into the layered piezoelectric element ofFIG. 15 or FIG. 17.

Thereby, the warp of a layered piezoelectric element generated at thetime of baking or polarizing the layered piezoelectric element can bereduced, thus preventing problems caused by the warp of the layeredpiezoelectric element at the time of manufacturing an ink-jet head, suchas inability to hold a piezoelectric body by air suction and peeling ofan adhesive agent caused by stress in the warp direction at the time ofbonding the layered piezoelectric element to a base.

Sixth Embodiment

Next, a description will be given, with reference to FIG. 19, of amethod of manufacturing the layered piezoelectric element 12 accordingto a sixth embodiment of the present invention. FIG. 19 is a sectionalview of the unprocessed layered piezoelectric element 32 according tothe manufacturing method of the sixth embodiment.

According to the manufacturing method of the sixth embodiment, a dummyinternal electrode 35 having substantially the same pattern shape as theinternal electrode 30 is formed in the dummy part 33 of the unprocessedlayered piezoelectric element 32 so that the dummy internal electrode 35and the internal electrode 30 are substantially in symmetricalpositions. In the case of forming the layered piezoelectric element 12of FIG. 15, it is preferred that the dummy internal electrode 35 beformed to have substantially the same pattern shape as the internalelectrode 31 so that the dummy internal electrode 35 and the internalelectrode 31 are substantially in symmetrical positions. In the case offorming the internal electrodes 30 in a plurality of layers, it ispreferable to form the dummy internal electrodes 35 in a plurality oflayers.

Thereby, the symmetry of the unprocessed layered piezoelectric element32 is improved further than by the manufacturing method of the fifthembodiment. Therefore, the warp of a layered piezoelectric elementgenerated at the time of baking or polarizing the layered piezoelectricelement can be further reduced, thus further preventing problems causedby the warp of the layered piezoelectric element at the time ofmanufacturing an ink-jet head, such as inability to hold a piezoelectricbody by air suction and peeling of an adhesive agent caused by stress inthe warp direction at the time of bonding the layered piezoelectricelement to a base.

Seventh Embodiment

Next, a description will be given, with reference to FIG. 20, of amethod of manufacturing the layered piezoelectric element 12 accordingto a seventh embodiment of the present invention. FIG. 20 is a sectionalview of the unprocessed layered piezoelectric element 32 according tothe manufacturing method of the seventh embodiment.

According to the manufacturing method of the seventh embodiment, a dummyinternal electrode 36 is formed in the dummy part 33 of the unprocessedlayered piezoelectric element 32 so as to have the same pattern shape asan internal electrode that alternates with an internal electrode 22Athat is closest to the surface of the layered piezoelectric element 12into which the unprocessed layered piezoelectric element 32 isprocessed. That is, in this case, the dummy internal electrode 36 isformed to have the pattern shape as the internal electrode 22B. Aspreviously described, the internal electrode 31 has the same patternshape as the internal electrode 22A.

By thus forming the dummy internal electrode 36, the layering orderpattern of internal electrodes can be simplified. Thereby, the number ofwasted internal electrodes can be reduced at the time of manufacturingthe layered piezoelectric element 12.

That is, in the case of forming the dummy internal electrode 36 and theinternal electrode 22B into the same shape and forming the internalelectrode 31 and the internal electrode 22A into the same shape, theinternal electrodes are layered from top to bottom in the order as shownin FIG. 21A. In FIGS. 21A and 21B, “A” refers to an internal electrodehaving the same pattern shape as the internal electrode 22A, and “B”refers to an internal electrode having the same pattern shape as theinternal electrode 22B. Generally, when internal electrodes arecategorized in two types by pattern shape, the two types of internalelectrodes alternate with each other in being printed due to theirprinting method. In this case, each piezoelectric element includes onepart of successive “A”s where the internal electrodes “A” aresuccessively layered. Therefore, the internal electrode “B” formedbetween the successive internal electrodes “A” is wasted.

On the other hand, in the case of forming the dummy internal electrode36 as well as the internal electrode 31 into the same shape as theinternal electrode 22A, the internal electrodes are layered from top tobottom in the order as shown in FIG. 21B. In this case, two parts ofsuccessive “A”s are formed in each piezoelectric element and one part ofsuccessive “A”s is formed between each adjacent piezoelectric elements,so that each piezoelectric element includes three successive-“A” partsin total. Therefore, three layers of internal electrodes “B” are wastedper piezoelectric element.

Eighth Embodiment

Next, a description will be given, with reference to FIG. 22, of anink-jet head as a liquid droplet ejecting head according to an eighthembodiment of the present invention. FIG. 22 is a sectional view of thelayered piezoelectric element 12 of the ink-jet head taken along thedirections in which the pressure liquid chamber thereof extendsaccording to the eighth embodiment. The layered piezoelectric element 12according to this embodiment includes an external electrode 40 forconduction having the same planar shape as the piezoelectric element 12.The external electrode 40 is formed on a surface of the layeredpiezoelectric element 12 which surface is not divided by the groovingprocessing so as to be connected to the common external electrode 23.

The external electrode 40 is not divided by the grooving processing.Therefore, the channel of electricity widens greatly on the commonelectrode side so that the common electrode resistance can be reduced.The external electrode 40 may have any shape as long as the externalelectrode 40 is connectable to the common external electrode 23 of thedriving parts 25 after the grooving processing. The wider the externalelectrode 40, the greater the desired effect of reduction in the commonelectrode resistance.

By thus providing the external electrode 40 that is not divided by thegrooving processing so that the external electrode 40 is connected tothe common external electrode 23, the common electrode resistance isreduced, so that the difference between the time constant of the drivingvoltage P_(v) applied to the layered piezoelectric element 12 in thecase of driving one of the channels and that in the case of driving allthe channels can be set to a value smaller than or equal to 2 μm.Thereby, the difference in the ejection characteristic can be reduced,so that a stable high-quality image can be obtained.

Ninth Embodiment

Next, a description will be given, with reference to FIG. 23, of anink-jet head as a liquid droplet ejecting head according to a ninthembodiment of the present invention. FIG. 23 is a sectional view of theink-jet head taken along the directions in which the pressure liquidchamber 6 thereof extends according to this embodiment.

The ink-jet head of this embodiment has the nozzles 5, the pressureliquid chambers 6 and the other liquid chambers, and the layeredpiezoelectric elements 12 arranged in two lines, respectively. In thisembodiment, the layered piezoelectric elements 12 of the secondembodiment are employed, but the layered piezoelectric elements 12according to any of the other embodiments may be employed.

Next, a description will be given, with reference to FIGS. 24 and 25, ofan ink-jet recording apparatus including the ink-jet head according tothe ninth embodiment of the present invention. FIG. 24 is a perspectiveview of the ink-jet recording apparatus, and FIG. 25 is a side view ofthe ink-jet recording apparatus, showing a mechanism part thereof.

The ink-jet recording apparatus includes a print mechanism part 112 in arecording apparatus main body 111. The print mechanism part 112 isformed of a carriage 123 movable in the primary scanning direction, arecording head formed of the ink-jet heads of the present invention andmounted in the carriage 123, and ink cartridges 125 supplying ink to therecording head. A paper feed cassette (or a paper feed tray) 114 capableof containing multiple sheets of paper 113 can be detachably attached tothe lower part of the main body 111 from the front side or the Y₂ sidein FIGS. 24 and 25. A manual feed tray 115 for manually feeding thepaper sheets 113 can be turned and opened. The paper sheet 113 fed fromthe paper feed cassette 114 or the manual feed tray 115 is loaded sothat a required image is recorded thereon by the print mechanism part112. Thereafter, the paper sheet 113 is ejected onto a paper ejectiontray 116 attached to the backside or the Y₁ side of the main body 111.

In the print mechanism part 112, the carriage 123 is held slidably inthe primary scanning direction by a primary guide rod 121 and asecondary guide rod 122 that are guide members extending betweenopposing side plates (not shown in the drawings). The primary scanningdirection corresponds to the directions in which the primary andsecondary guide rods 121 and 122 extend. That is, the primary scanningdirection corresponds to the X-axis in FIGS. 24 and 25. Heads 124 formedof the ink-jet heads (liquid droplet ejecting heads) of the presentinvention ejecting yellow (Y) ink, cyan (C) ink, magenta (M) ink, andblack (Bk) ink, respectively, are attached to the carriage 123 so that aplurality of ink ejection openings thereof are arranged in thedirections to cross the primary scanning direction and ink is ejectedfrom the ink ejection openings in the downward direction. The FPC cable14 is connected between the heads 124 and a controller part 150 so as toapply a driving waveform to each of the heads 124. The FPC cable 14exchanges signals between the heads 124 and the controller part 150.

The ink cartridges 125 for supplying the respective color inks to thecorresponding heads 124 are attached replaceably to the carriage 123.Each ink cartridge 125 has a vent formed in its upper part and a supplyopening formed in its lower part. The vent communicates with theatmosphere. Ink is supplied from each ink cartridge 125 through itssupply opening to the corresponding head 124. Further, each inkcartridge 125 includes a porous body filled with ink so that the inksupplied to the corresponding head 124 is maintained at a slightlynegative pressure by the capillary force of the porous body.

The heads 124 for the respective color inks employed as a recording headin this embodiment may be replaced by a single head including nozzlesfor ejecting ink droplets of the respective color inks.

The primary guide rod 121 penetrates through the rear (Y₁-side) part(part on the downstream side in the direction in which the paper sheet113 is conveyed) of the carriage 123 so that the cartridge 123 can slidealong the primary guide rod 121. The front (Y₂-side) part (part on theupstream side in the direction in which the paper sheet 113 is conveyed)of the carriage 123 is placed on the secondary guide rod 122 so that thecarriage 123 can slide along the secondary guide rod 122. A timing belt130 is extended between a drive pulley 128 rotated by a primary scanningmotor 127 and a driven pulley 129. The timing belt 130 is fixed to thecarriage 123 so that the carriage 123 is moved back and forth forscanning along the primary scanning direction by the reverse and forwardrotations of the primary scanning motor 127.

On the other hand, in order to convey each paper sheet 113 set in thepaper feed cassette 114 to a position below the heads 124, the ink-jetrecording apparatus includes a paper feed roller 131 and a friction pad132 for separating each paper sheet 113 from the paper feed cassette114, a guide member 133 for guiding each paper sheet 113, a conveyanceroller 134 conveying each fed paper sheet 113 upside down, a roller 135pressed against the outside surface of the conveyance roller 134, and atip roller 136 defining an angle at which each paper sheet 113 is sentfrom the conveyance roller 134. The conveyance roller 134 is rotated bya secondary scanning motor 137 via a gear train.

Further, the ink-jet recording apparatus includes a printing receptionmember 139 that is a sheet guide member guiding each paper sheet 113sent from the conveyance roller 134 below the heads 124. The guide rangeof the printing reception member 139 corresponds to the movement rangeof the carriage 123 in the primary scanning direction. On the downstreamside of the printing reception member 139 in the direction in which eachpaper sheet 113 is conveyed, the ink-jet recording apparatus includes aconveyance roller 141 and a spur 142 rotated to send each paper sheet113 in a direction to eject each paper sheet 113, and further includesan ejection roller 143 and a spur 144 for sending out each paper sheet113 onto the paper ejection tray 116 and guide members 145 and 146forming a paper ejection path through which each paper sheet 113 isconveyed to be ejected.

At the time of recording, the heads 124 are driven in accordance with animage signal with the carriage 123 being moved. Thereby, ink is ejectedonto the stationary paper sheet 113 so that recording is performed forone line. Then, after the paper sheet 113 is conveyed a predetermineddistance, recording is performed for the next line. When a recording endsignal or a signal indicating that the trailing edge of the paper sheet113 has reached the recording region is received, the recordingoperation is terminated so that the paper sheet 113 is ejected. In thiscase, since each of the ink-jet heads of the present invention formingthe heads 124 has improved controllability of ink droplet ejection,thereby suppressing variation in its characteristic, the ink-jetrecording apparatus can record a stable high-quality image.

Further, the ink-jet recording apparatus includes a recovery part 147for recovering from ejection failure in the heads 124. The recovery part147 is provided on the X₁ side in the moving directions of the carriage123 in a position outside the recording region as shown in FIG. 24. Therecovery part 147 includes a capping part, a suction part, and acleaning part. While waiting for printing, the carriage 123 is moved tothe recovery part (147) side so as to have the heads 124 capped by thecapping part. Thereby, the ink ejection openings of the heads 124 aremaintained in a moist state, so that ejection failure due to drying isprevented. Further, during a recording operation, ink irrelevant to therecording is ejected so that all the ink ejection openings have the sameink viscosity, thereby maintaining a stable ejection characteristic.

In the case of the occurrence of ejection failure, the ink ejectionopenings (nozzles 5) of the heads 124 are hermetically sealed by thecapping part, and air bubbles as well as ink are evacuated from the inkejection openings through a tube by the suction part. Ink or dustadhering to the ink ejection surface of each head 124 is removed by thecleaning part. Thereby, the heads 124 recover from ejection failure. Theevacuated ink is ejected to a waste ink reservoir (not shown in thedrawings) provided in a lower part of the main body 111. In the wasteink reservoir, the waste ink is absorbed and kept in an ink absorbingbody.

Thus, the ink-jet recording apparatus of this embodiment includes theink-jet heads of the present invention. Therefore, the differencebetween the time constant of the case of driving one channel and thetime constant of the case of driving all channels can be reduced, sothat a stable high-quality image can be recorded.

In the above-described embodiments, the present invention is applied toan ink-jet head as a liquid droplet ejecting head. However, the presentinvention is also applicable to liquid droplet ejecting heads other thanthe ink-jet head, such as a liquid droplet ejecting head ejectingdroplets of a liquid resist and a liquid droplet ejecting head ejectingdroplets of a DNA sample.

Further, in the above-described embodiments, the present invention isapplied to the actuator part (pressure generating part), as apiezoelectric actuator, of a liquid droplet ejecting head such as anink-jet head. However, the present invention is also applicable to amicroswitch (a micro relay), an actuator for a multi-optical lens (anoptical switch), a micro flow meter, and a pressure sensor as well as amicropump and an optical device (an optical modulator).

Further, in the above-described embodiments, the present invention isapplied to a side-shooter head in which the direction in which adiaphragm is displaced is equal to the direction in which an ink dropletis ejected. However, the present invention is also applicable to anedge-shooter head in which the direction in which a diaphragm isdisplaced is perpendicular to the direction in which an ink droplet isejected.

The present invention is not limited to the specifically disclosedembodiments, but variations and modifications may be made withoutdeparting from the scope of the present invention.

The present application is based on Japanese priority application No.2002-047371 filed on Feb. 25, 2002, the entire contents of which arehereby incorporated by reference.

1. A layered piezoelectric element comprising: a plurality of drivingparts divided by grooves, the driving parts comprising alternate layersof piezoelectric layers and internal electrodes; and non-driving partsformed at both ends of an array of said driving parts, the non-drivingparts comprising the alternate layers of the piezoelectric layers andthe internal electrodes, wherein a common electrode of said drivingparts is extended from said non-driving parts; and a difference betweena time constant of a driving voltage applied to the layeredpiezoelectric element in a case of driving all of said driving parts anda time constant of a driving voltage applied to the layeredpiezoelectric element in a case of driving one of said driving parts issmaller than or equal to 2 μsec.
 2. A piezoelectric actuator comprising:a movable part; and a layered piezoelectric element performing saidmovable part, the layered piezoelectric element comprising: a pluralityof driving parts divided by grooves, the driving parts comprisingalternate layers of piezoelectric layers and internal electrodes; andnon-driving parts formed at both ends of an array of said driving parts,the non-driving parts comprising the alternate layers of thepiezoelectric layers and the internal electrodes, wherein a commonelectrode of said driving parts is extended from said non-driving parts;and a difference between a time constant of a driving voltage applied tothe layered piezoelectric element in a case of driving all of saiddriving parts and a time constant a driving voltage applied to thelayered piezoelectric element in a case of driving one of said drivingparts is smaller than or equal to 2 μsec.
 3. A liquid droplet ejectinghead comprising: a piezoelectric actuator pressurizing a liquid chambercommunicating with a nozzle so as to eject a liquid droplet from thenozzle, the piezoelectric actuator comprising a layered piezoelectricelement, the layered piezoelectric element comprising: a plurality ofdriving parts divided by grooves, the driving parts comprising alternatelayers of piezoelectric layers and internal electrodes; and non-drivingparts formed at both ends of an array of said driving parts, thenon-driving parts comprising the alternate layers of the piezoelectriclayers and the internal electrodes, wherein a common electrode of saiddriving parts is extended from said non-driving parts; and a differencebetween a time constant of a driving voltage applied to the layeredpiezoelectric element in a case of driving all of said driving parts anda time constant of a driving voltage applied to the layeredpiezoelectric element in a case of driving one of said driving parts issmaller than or equal to 2 μsec.
 4. An ink-jet recording apparatuscomprising: an ink-jet head ejecting an ink droplet, the ink-jet headcomprising a piezoelectric actuator pressurizing a liquid chambercommunicating with a nozzle so as to eject the ink droplet from thenozzle, the piezoelectric actuator comprising a layered piezoelectricelement, the layered piezoelectric element comprising: a plurality ofdriving parts divided by grooves, the driving parts comprising alternatelayers of piezoelectric layers and internal electrodes; and non-drivingparts formed at both ends of an array of said driving parts, thenon-driving parts comprising the alternate layers of the piezoelectriclayers and the internal electrodes, wherein a common electrode or saiddriving parts is extended from said non-driving parts; and a differencebetween a time constant of a driving voltage applied to the layeredpiezoelectric element in a case of driving all of said driving parts anda time constant of a driving voltage applied to the layeredpiezoelectric element in a case of driving one of said driving parts issmaller than or equal to 2 μsec.
 5. An ink-jet recording apparatuscomprising: an ink-jet head, the ink-let head comprising a layeredpiezoelectric element pressurizing a liquid chamber so as to eject anink droplet therefrom, the layered piezoelectric element comprising: aplurality of driving parts divided by grooves, the driving partscomprising alternate layers of piezoelectric layers and internalelectrodes; and non-driving parts formed at both ends of an any of saiddriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrodes, wherein a commonelectrode of said driving parts is extended from said non-driving parts;and a difference between a time constant of a driving voltage applied tothe layered piezoelectric element in a case of driving all of saiddriving parts and a time constant of a driving voltage applied to thelayered piezoelectric element in a case of driving one of said drivingparts is smaller than or equal to 2 μsec.
 6. A layered piezoelectricelement comprising: a plurality of driving parts divided by grooves, thedriving parts Comprising alternate layers of piezoelectric layers andinternal electrodes; non-driving parts formed at both ends of an arrayof said driving parts, the non-driving parts comprising the alternatelayers of the piezoelectric layers and the internal electrodes; and aninternal electrode for conduction connected to a common externalelectrode of said driving parts and undivided by the grooves, wherein acommon electrode of said driving parts is extended from said non-drivingparts.
 7. The layered piezoelectric element as claimed in claim 6,wherein said internal electrode for conduction has a shape substantiallyequal to a shape that one of the internal electrodes of the alternatelayers has before the alternate layers are grooved.
 8. The layeredpiezoelectric clement as claimed in claim 6, wherein said internalelectrode for conduction is formed in a plurality of layers.
 9. Thelayered piezoelectric element as claimed in claim 8, wherein each of thelayers of said internal electrode for conduction has a shapesubstantially equal to a shape that one of the internal electrodes ofthe alternate layers has before the alternate layers are grooved.
 10. Apiezoelectric actuator comprising: a movable part; and a layeredpiezoelectric element deforming said movable part, the layeredpiezoelectric element comprising: a plurality of driving parts dividedby grooves, the driving parts comprising alternate layers ofpiezoelectric layers and internal electrodes; non-driving parts formedat both ends of an array of said driving parts, the non-driving partscomprising the alternate layers of the piezoelectric layers and theinternal electrodes; and an internal electrode for conduction connectedto a common external electrode of said driving parts and undivided bythe grooves, wherein a common electrode of said driving parts isextended from said non-driving parts.
 11. The piezoelectric actuator asclaimed in claim 10, wherein said internal electrode fur conduction hasa shape substantially equal to a shape that one of the internalelectrodes of the alternate layers has before the alternate layers aregrooved.
 12. The piezoelectric actuator as claimed in claim 10, whereinsaid internal electrode for conduction is formed in a plurality oflayers.
 13. The piezoelectric actuator as claimed in claim 12, whereincatch of the layers of said internal electrode for conduction has ashape substantially equal to a shape that one of the internal electrodesof the alternate layers has before the alternate layers are grooved. 14.A liquid droplet ejecting head comprising: a piezoelectric actuatorpressurizing a liquid chamber communicating with a nozzle so as to ejecta liquid droplet from the nozzle, the piezoelectric actuator comprisinga layered piezoelectric element, the layered piezoelectric elementcomprising: a plurality of driving parts divided by grooves, the drivingparts comprising alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of saiddriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrodes; and an internalelectrode for conduction connected to a common external electrode ofsaid driving parts and undivided by the grooves, wherein a commonelectrode of said driving parts is extended from said non-driving parts.15. The liquid droplet ejecting head as claimed in claim 14, whereinsaid internal electrode for conduction has a shape substantially equalto a shape that one of the internal electrodes of the alternate layershas before the alternate layers are grooved.
 16. The liquid dropletejecting head as claimed in claim 14, wherein said internal electrodefor conduction is formed in a plurality of layers.
 17. The liquiddroplet ejecting head as claimed in claim 16, wherein each of the layersof said internal electrode for conduction has a shape substantiallyequal to a shape that one of the internal electrodes of the alternatelayers has before the alternate layers are grooved.
 18. An ink-jetrecording apparatus comprising: an ink-jet head ejecting an ink droplet,the ink-jet head comprising a piezoelectric actuator pressurizing aliquid chamber communicating with a nozzle so as to eject the inkdroplet from the nozzle, the piezoelectric actuator comprising a layeredpiezoelectric element, the layered piezoelectric element comprising: aplurality of driving parts divided by grooves, the driving partscomprising alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of saiddriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrodes; and an internalelectrode for conduction connected to a common external electrode ofsaid driving parts and undivided by the grooves, wherein a commonelectrode of said driving parts is extended from said non-driving parts.19. The ink-jet recording apparatus as claimed in claim 18, wherein saidinternal electrode for conduction has a shape substantially equal to ashape that one of the internal electrodes of the alternate layers hasbefore the alternate layers are grooved.
 20. The ink-jet recordingapparatus as claimed in claim 18, wherein said internal electrode forconduction is formed in a plurality of layers.
 21. The ink-jet recordingapparatus as claimed in claim 20, wherein each of the layers of saidinternal electrode for conduction has a shape substantially equal to ashape that one of the internal electrodes of the alternate layers hasbefore the alternate layers.
 22. A layered piezoelectric elementcomprising: a plurality of driving parts divided by grooves, the drivingparts comprising alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of saiddriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrodes; and an externalelectrode for conduction connected to a common external electrode ofsaid driving parts, the external electrode for conduction being formedon a stance of the layered piezoelectric layer which surface isundivided by the grooves, wherein a common electrode of said drivingparts is extended from said non-driving parts.
 23. A piezoelectricactuator comprising: a movable part; and a layered piezoelectric elementdeforming said movable part, the layered piezoelectric elementcomprising: a plurality of driving parts divided by grooves, the drivingparts comprising alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of saiddriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrodes: and an externalelectrode for conduction connected to a common external electrode ofsaid driving parts, the external electrode for conduction being formedon a surface of the layered piezoelectric layer which surface isundivided by the grooves, wherein a common electrode of said drivingparts is extended from said non-driving parts.
 24. A liquid dropletejecting head comprising: a piezoelectric actuator pressurizing a liquidchamber communicating with a nozzle so as to eject a liquid droplet fromthe nozzle, the piezoelectric actuator comprising a layeredpiezoelectric element, the layered piezoelectric element comprising: aplurality of driving parts divided by grooves, the driving partscomprising alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of saiddriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrocles; and an externalelectrode for conduction connected to a common external electrode ofsaid driving parts, the external electrode for conduction being formedon a surface of the layered piezoelectric layer which surface isundivided by the grooves, wherein a common electrode of said drivingparts is extended from said non-driving parts.
 25. An ink-jet recordingapparatus comprising: an ink-jet head ejecting an ink droplet, theink-jet head comprising a piezoelectric actuator pressurizing an inkchamber communicating with a nozzle so as to eject the ink droplet fromthe nozzle, the piezoelectric actuator comprising a layeredpiezoelectric element, the layered piezoelectric element comprising: aplurality of driving parts divided by grooves, the driving partscomprising alternate layers of piezoelectric layers and internalelectrodes; non-driving parts formed at both ends of an array of saiddriving parts, the non-driving parts comprising the alternate layers ofthe piezoelectric layers and the internal electrodes: and an externalelectrode for conduction connected to a common external electrode ofsaid driving parts, the external electrode for conduction being formedon a surface of the layered piezoelectric layer which surface isundivided by the grooves, wherein a common electrode of said drivingparts is extended from said non-driving parts.
 26. A method ofmanufacturing a layered piezoelectric element including a plurality ofdriving parts divided by grooves, non-driving parts formed at both endsof an array of the driving parts, and an internal electrode forconduction connected to a common external electrode of the driving partsand undivided by the grooves, the driving parts and the non-drivingparts comprising alternate layers of piezoelectric layers and internalelectrodes, the driving parts having a common electrode extended fromthe non-driving parts, the method comprising the steps of: (a) fixing amember including a dummy part to a base, the dummy part being formed ofa piezoelectric layer to have a shape substantially symmetrical to ashape of a group of the internal electrodes of the alternate layers in adirection in which the alternate layers are formed; and (b) removing thedummy part from the member.
 27. The method us claimed in claim 26,wherein a dummy internal electrode corresponding to the internalelectrode for conduction is formed in the dummy part.
 28. The method asclaimed in claim 27, wherein the dummy internal electrode has a shapesymmetrical to a shape that one of the internal electrodes of thealternate layers has before the alternate layers are grooved, the one ofthe internal electrodes being closest to a surface of the member afterthe dummy part is removed therefrom, the surface of the member beingcreated by removing the dummy part.
 29. The method as claimed in claim27, wherein the dummy internal electrode has a shape substantiallysymmetrical to a shape that a first one of the internal electrodes ofthe alternate layers has before the alternate layers are grooved, thefirst one of the internal electrodes alternating with a second one ofthe internal electrodes of the alternate layers, the second one of theinternal electrodes being closest to a surface of the member after thedummy part is removed therefrom, the surface of the member being createdby removing the dummy part. are grooved.